0, hashset add will return false, hence we find out if sudoku is valid or not.

We can create a key in Hashset based on the check we are performing. For eg.

Check number in row - '4' in row 7
Check number in column - '4' in column 7
Check number in grid 9 (for row 7, column 7), can be '4' in grid 7/3-7/3

The add method of Set returns true if this set did not already contain the specified element (i.e., the current number in that row, column, or subgrid); if it's false, this means we've encountered a duplicate number in the same row, column, or subgrid, and thus the Sudoku board is not valid. Therefore, the method will return false.

Code

[{"language":"Java","code":"class Solution {\n\n\tpublic boolean isValidSudoku(char[][] board) {\n\t\tSet<String> seen = new HashSet<>();\n\n\t\tfor (int i = 0; i < 9; ++i) {\n\t\t\tfor (int j = 0; j < 9; ++j) {\n\t\t\t\tchar number = board[i][j];\n\n\t\t\t\tif (number == '.') {\n\t\t\t\t\tcontinue;\n\t\t\t\t}\n\n\t\t\t\tif (!seen.add(number + \" in row \" + i) ||\n\t\t\t\t\t!seen.add(number + \" in column \" + j) ||\n\t\t\t\t\t!seen.add(number + \" in block \" + i / 3 + \"-\" + j / 3)) {\n\t\t\t\t\treturn false;\n\t\t\t\t}\n\t\t\t}\n\t\t}\n\n\t\treturn true;\n\t}\n}","lang":"java","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span style=\"color:#24292E;--s

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